Behaviour of simple ions in the system cellulose–anionic dye–simple electrolyte. Part 1.—Partition equilibria

Abstract

The partition equilibria of Na⁺ and Cl^– between a cellulose membrane and an aqueous bath have been studied mainly as a function of the concentration of electrolyte and of ionised acid groups fixed in the membrane. The latter concentration could be varied by the adsorption of suitable amounts of the dye Direct Blue 1. The observed ionic partition behaviour is difficult to reconcile with the standard simple equipotential volume model (EVM) treatment, even allowing for such effects as imperfect experimental separation of membrane and aqueous phases. The EVM with the additional assumption of “cation binding” by the fixed anionic groups can explain the results only empirically. On the other hand, a non-equipotential volume pore model appears to offer a physically more meaningful and acceptable interpretation. However, the single uniformly charged pore model of Schofield et al. requires further elaboration in order to explain the partition behaviour at higher dilution.